The immune system in higher vertebrates is the first line of defence against various antigens that can enter the vertebrate body, including micro-organisms such as bacteria, fungi and viruses that are the causative agents of a variety of diseases. Moreover, the immune system is also involved in a variety of other diseases or disorders, including autoimmune or immunopathologic diseases, immunodeficiency syndromes, atherosclerosis and various neoplastic diseases. Although methods are available for treating these diseases, many current therapies provide less than adequate results, and carry the risk of significant side effects. Among new emergent therapeutic strategies, those based on cell therapy appear to constitute a potentially useful tool for treating a great number of diseases. Thus, a great effort is currently being made by researchers in order to achieve said aim.
Autoimmune Diseases
Autoimmune diseases are caused when the body's immune system, which is meant to defend the body against bacteria, viruses, and any other foreign product, malfunctions and produces a pathological response against healthy tissue, cells and organs.
T cells and macrophages provide beneficial protection, but can also produce harmful or deadly immunological responses. Autoimmune diseases can be organ specific or systemic and are provoked by different pathogenic mechanisms. Systemic autoimmune diseases involve polyclonal B cell activation and abnormalities of immunoregulatory T cells, T cell receptors and MHC genes. Examples of organ specific autoimmune diseases are diabetes, hyperthyroidism, autoimmune adrenal insufficiency, pure red cell anemia, multiple sclerosis and rheumatic carditis. Representative systemic autoimmune diseases include systemic lupus erythematosus, chronic inflammation, Sjogren's syndrome, polymyositis, dermatomyositis and scleroderina.
Current treatment of autoimmune diseases involves administering immunosuppressive agents such as cortisone, aspirin derivatives, hydroxychloroquine, methotrexate, azathioprine and cyclophosphamide or combinations thereof. The dilemma faced when administering immunosuppressive agents, however, is that the more effectively the autoimmune disease is treated, the more defenseless the patient is left to attack from infections, and the more susceptible the patient is to developing tumors. Thus, there is a great need for new therapies for the treatment of autoimmune diseases.
Inflammatory Disorders
Inflammation is a process by which the body's white blood cells and secreted factors protect our bodies from infection by foreign substances, such as bacteria and viruses, and is a common process in autoimmune diseases. Secreted factors known as cytokines and prostaglandins control this process, and are released in an ordered and self-limiting cascade into the blood or affected tissues. In general, the current treatments for chronic inflammatory disorders have a very limited efficiacy, and many of them have a high incidence of side effects or cannot completely prevent disease progression So far, no treatment is ideal, and there is no cure for these type of pathologies. Thus, there is a great need for new therapies for the treatment of inflammatory disorders.
Inhibition of T-Cell Responses
All immune responses are controlled by T cells. Self-reactive cells with the potential to elicit autoimmune responses comprise a part of the normal T cell repertoire, but in the healthy state, their activation is prevented by suppressor cells. Although T suppressor cells were originally described in the 1970s, significant progress in characterizing T-cell subsets has been made only recently, when they have been renamed as regulatory T cells.
There are different CD4+, CD8+, natural killer cell, and gamma and delta T cell subsets with regulatory (suppressor) activity. Two major types of T-reg cells have been characterized in the CD4+ population, i.e., the naturally-occurring, thymus-generated T-reg cells, and the peripherally-induced, IL-10 or TGF-beta secreting T-reg cells (Trl cells). The CD4+CD25+, Foxp3 -expressing, naturally-occurring T-reg cells generated in thymus, migrate and are maintained in the periphery.
Cell Therapy
Regulatory T-cell administration has long been identified as having significant potential in addressing key causes of immune and inflammatory disorders. However, there are currently no preparation protocols suitable for use in the large scale manufacture of regulatory T-cells and accordingly clinical development of regulatory T-cell therapies has been severely limited.
Mesenchymal stem cells (MSCs) are multipotent adult stem cells capable of differentiation into mesenchymal-type cells (adipocytes, osteoblasts and chondrocytes), but also myocytes, neurons, endothelial cells, astrocytes and epithelial cells. Although first reported in the normal adult bone marrow (BM-MSC), MSCs can also be obtained from other sources, such as umbilical cord blood, peripheral blood and adipose tissue. It has been observed that the in-vivo administration of mesenchymal stem cells appears to be associated with an upregulation of regulatory T-cells. Moreover, methods for the in-vitro preparation of T-reg cells (for their use in the treatment of immune and inflammatory disorders) are known in the art. For example PCT Patent Application WO2007039150 provides a method for the preparation of said cells by contacting mesenchymal stem cells with peripheral blood leukocytes. However, at present there still remains a long felt need for a means for the preparation of regulatory T-cells in a manner suitable for use in clinical as opposed to research applications.